1. Field of the Invention
The present invention relates to a wafer holding apparatus suitable for use in the automatic attachment and detachment of wafers to and from a susceptor unit in a process for the manufacture of a semiconductor device.
2 . Description of the Related Art
Generally the process for the manufacture of a semiconductor device includes a step for epitaxially forming a thin film on the surface of a wafer. The epitaxial step comprises attaching wafers to wafer support grooves in a susceptor made of carbon, heating each wafer in a reaction furnace and forming a desired thin film while supplying a predetermined gas in the reaction furnace. In this case, the attachment and detachment of the wafer to and from the susceptor are achieved using a wafer holding apparatus.
This type of wafer holding apparatus has conventionally been constructed as shown, for example, in FIG. 1. During the operation of the apparatus, a chuck body 5 fixed to the forward end of a transfer arm 6 is moved between a standby station 9 having wafers 7 waiting for treatment and the susceptor 2 so that the wafer is transferred. The wafer 7 is held by claws 3 mounted by air cylinders 4 on the chuck body 5. The attachment and detachment of the wafer 7 to and from a wafer support groove 8 in the susceptor 2 are effected by opening and closing the chuck claws 3 by means of air cylinders 4. The wafer holding position of the chuck claw 3 and wafer placing position at the wafer support groove 8 of the susceptor 2 are initially set up by coinciding the stop position of the transfer arm 6 with that of the susceptor 2 side and these positions are provided as fixed positions.
In FIG. 1, reference numeral 1 shows a support plate for supporting six susceptors 2 arranged, for example, in a hexagonal configuration.
The aforementioned wafer holding apparatus is of such a type that the wafer 7 is attached and detached to and from the wafer support groove 8 in the susceptor 2 with the chuck body 5 fixed to the forward end of the transfer arm 6. In this case, the wafer 7 held by the chuck claws 3 on the wafer 7 side is held at all times in a fixed position.
The susceptor 2 is held in position such that it is suspended in a manner to surround the outer periphery of the hexagonal support plate 1. The attachment and detachment of the wafer 7 are sequentially effected relative to six susceptors at a time by rotating the support plate 1. During the process of manufacture, a manufacturing error, though being somewhat slight, is produced between the susceptor 2 and the support plate 1. Relative to the wafer 7 held on the susceptor 2 side by the chuck claws 3, the wafer support groove 8 is not located at all times in a predetermined position for a reason as set out above and some positional displacement is produced, upon attachment, relative to the individual susceptor 2.
The positional displacement causes a misalignment to be produced between the wafer and the wafer support groove 8. As a result, a clearance is produced between the susceptor 2 and the wafer 7, dropping the wafer 7 out of the wafer support groove 8 and causing damage to the wafer. Upon detachment, the wafer 7 cannot be properly held by the chuck claws 3 and the wafer 7 is dropped out of the groove 8 and suffers damage.
It is usually desirable that a thin film treatment be effected in an intimate wafer-to-susceptor contact state. Any clearance, if being produced, causes a poor or defective film to be formed on the wafer 7.